This invention relates to an improved method and apparatus for comminuting tree stumps and buried roots while in the ground surface.
In one conventional land clearing operation, tree stumps remaining after felling trees are lifted out of the ground and moved to the side by means of tracked vehicles or other suitable apparatus where they are left to rot or be transported away to a dump or other disposal area. This procedure has considerable disadvantages. If the tree stumps remain at a collection point, they take up space which thus becomes unusable. Transporting the tree stumps away involves additional cost for labor and vehicles. If the stump is moved aside from its original, rooted position it causes simultaneous removal of valuable top soil which is necessary in situations where trees are to be replanted in the cleared area. In addition, when the hole caused by removal of the stump, is filled, top soil is moved deep into the ground where it is useless for new plantings, while conversely a larger quantity of uncultivated soil, such as clay and sand without humus, is brought to the surface. Uprooting of the tree stumps may also result in severe damage to the root system which is important in situations where the cleared land is to be replanted for growing new trees. The aforementioned conventional practice also places a greater load on waste disposal areas which are already severely overcrowded.
In another conventional practice of stump removal, the stumps are uprooted and burned on site.
This is not only costly and dangerous from the standpoint of fire prevention but furthermore, the products of combustion polute the air and add to the ecology problem which today is so very urgent. Already in some areas laws and regulations have been passed restricting burning operations in an effort to increase fire safety as well as to reduce air pollution. Such restricted burning conditions still do not entirely solve the pollution problem and in any event, make stump removal by burning a slow and expensive operation.
In an attempt to overcome these disadvantages, various methods and apparatus have been developed to comminute tree stumps rooted in the ground. For example U.S. Pat. No. 1,312,450 discloses a milling apparatus for cutting tree trunks employing a rotating milling roller lowered onto the top of the stump for milling the wood of the stump away. However, with this patented apparatus, the milling process can be conducted only to a limited extent below the ground surface and as a result, the entire stump cannot be removed. Moreover in order to mill below the surface with this patented device, a milling roller which is wider in diameter in the middle must be used such that it is not possible to touch the lateral roots. Thus, during subsequent new cultivation or re-plantings, the place where the stump stood, as well as its immediate surrounding area, cannot be planted. In situations where the cleared land is not to be used for re-planting trees, the method and apparatus disclosed in U.S. Pat. No. 1,312,450 is still believed to be inadequate for commercial purposes because it involves cutting across the grain of the stump on the upper surface of the stump which requires excessive drum pressure and speed and moreover takes a relatively long time to cut through the entire stump. It also requires that the knives be sharpened very frequently. Furthermore it is doubted that the long knives used on this patented device would permit continuous rotation of the drum through the stump, but instead would cause periodic binding heaving or stoppage of the drum particularly when great pressure is exerted on the stump. Another serious deficiency with this patented device is that it cannot cut the stump below the ground surface because the drum bearing and pulley transmission system prevents it and would be subject to damage. Moreover soil would build up behind the knives preventing effective cutting action. Finally with respect to U.S. Pat. No. 1,312,450 it is noted that it discloses a very complicated and cumbersome mechanism for pressing the drum on the stump as the cutting operation proceeds.
Other prior art cutting method and apparatus which attempt to comminute stumps by cutting across the grain on the top surface of the stump, are also disclosed in U.S. Pat. Nos. 3,044,509 and 3,389,726. Additionally, these patented devices also cannot remove the entire stump because the distance the cutting roller can move below the ground surface is limited by the drum bearings and drive transmission. Furthermore the great weight required to effectively comminute a stump, particularly when cutting across the grain by rotating across the top face of the stump, is believed to be lacking from these patented devices. Moreover it has been discovered by applicant that an exceedingly high drum speed is required for effective comminution which if applied to the belt drive system disclosed in these patents, would cause periodic damage thereto, particularly since a great deal of vibration is encountered in comminuting a tree stump. The possibility of damaging such a conventional drive transmission is increased if the drum is operated below the ground surface.
It has further been discovered by applicant herein that it is difficult to maintain the cutting roller properly positioned on a tree stump when using a conventional arrangement of knives on the drum such as disclosed in U.S. Pat. Nos. 3,389,726 and 3,044,509. Moreover the spiral arrangement of the roller knives disclosed in U.S. Pat. No. 3,389,726 would cause the drum to "walk" laterally off the stump to frustrate the cutting operation. It is further noted that the cutting rollers disclosed in U.S. Pat. Nos. 3,044,509 and 3,389,726 are hitched to the rear of a vehicle so that any stumps or other obstacles encountered below the rear of the vehicle or under the hitch, could prevent proper contact of the drum with the stump to be removed. It would, of course, also hinder the manueverability of the vehicle and the drum.
Another known device for cutting tree stumps while rooted in the soil, is disclosed in German Pat. No. 1,945,388 (Gebrauchsmuster) and includes a milling disc equipped with cutting knives, with the axis of rotation of the disc extending in the same direction as the length of the vehicle. The disc is attached to the rear of a vehicle, and is lowered partially into the ground in front of the stump and then the disc is moved against the stump. However, the working depth and especially the height of tree stumps which can be attacked, are limited by the diameter of the milling disc. The milling disc engages the stump only in its lower reaches, so that considerable lateral forces are exerted upon the vehicle which tend to overturn the vehicle. The soil and wood are thrown off laterally, without filling the hole produced by the cutting operation. Since the cutting forces on the tree stump are primarily horizontal, the stump tends to move laterally away from the cutter disc. In the vicinity of the disc axis, where the largest quantity of wood must be broken up, the cutting speed is too slow for effective cutting of the wood. Applicant is familiar with this device being one of the coinventors named in said German Patent.
Another device employing cutter discs is shown in U.S. Pat. No. 3,625,267 which also involves a relatively slow process of cutting stumps and suffers from some of the same draw-backs mentioned above in connection with the above-cited German Patent. This device must make numerous vertical cuts in the stump in order to entirely remove the stump. Moreover, the bearings for the cutter discs and the chain drive are prone to damage since they directly engage the stump. The damage is enhanced when operating below the ground surface.
In addition to the shortcomings of prior patented devices summarized above, applicant has discovered that the roller knives of the prior art particularly those employing extremely hard material, such as carbide material, are prone to chipping and breakage upon encountering the tough, hard material of the stump with great impact. Also, constant sharpening of the roller knives is required which considerably slows the overall stump removal operation. Furthermore applicant has discovered that in order to obtain a balanced cutter drum which will not wander or walk off the stump or heave or stop during operation when pressure is applied to the stump, it is important to position the knives in a certain manner here-to-fore lacking from the prior art.
In summary, applicant believes that none of the prior art devices are adequate for continuous commercial use over long periods in removing entire tree stumps.